“In today’s world, even as we all cherish our sovereignty, the nations who wield their influence most effectively are the nations that do it through the collective action that today’s challenges demand.”

Ahead of his Downing Street summit the US President and wife Michelle will enjoy a birthday lunch with the Queen.

Obama will meet David Cameron for talks (Image: Reuters)

They will also dine with Prince William and Kate.

Polls show the President remains hugely popular in Britain after nearly eight years in office and 'Leave' campaigners are worried about the impact his comments may have.

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Ukip leader Nigel Farage said Mr Obama should "butt out".

“This is an unwelcome interference from the most anti-British American president there has ever been," Mr Farage said.

"Mercifully, he won't be in office for much longer."

Nigel Farage (Image: Reuters)

And former Cabinet Minister Iain Duncan Smith said he did not see how an intervention by the US leader in Britain’s affairs could be "appropriate".

But David Cameron said the President was "perfectly entitled" to set out his view.

He told BBC Radio Bristol: I do think it's good to listen to your allies and friends and America, who work with us so closely, who lost a lot of people in the First and Second World Wars fighting alongside the British.

"I think he is perfectly entitled to say 'as a friend of Britain, I'm not going to tell you what to do, I'm just going to tell you what I think'."

Last night another political heavyweight backed the 'Remain' campaign as former Labour PM Gordon Brown told an audience in London it is vital Europe sticks together to deal with the migration crisis and terror threat.

“Without a European Union policy for the Middle East, things will undoubtedly get worse,” Mr Brown said.

“If a European Union was not in existence it would have to be invented to deal with these problems on our doorstep.”

Gordon Brown

The former PM accepted immigration was a big issue for many voters and said both Brussels and the UK Government must do more to help areas affected by large numbers of new arrivals.

"The benefits of immigration are general - but the problems are very specific," he said.

"We have to do far more to help those communities that are in difficulty as a result of the pressures of numbers.”

He added that winning over Labour voters will be the key to keeping Britain in Europe and called on the 'Remain' campaign to be positive, passionate, principled and patriotic in the weeks running up to the June 23 poll.

“It would be a tragedy of those people who say Britain should leave the EU were identified as the patriotic group, and those who wanted to stay in were seen as standing up for Europe against Britain,” Mr Brown said.